The invention relates to new unsaturated cyclic organic compounds which can be used as monomers or co-monomers in free radical polymerisation and polymers or co-polymers derived from these compounds. These compounds have the ability to ring open during polymerisation and provide examples of allylic monomers that will readily polymerise to high molecular weight polymers.
Monomers capable of ring opening (hereinafter referred to as xe2x80x9cring-opening monomersxe2x80x9d) are important in minimising volume shrinkage during polymerisation. Additionally, ring-opening monomers are useful in providing an alternative method of incorporating functionalities such as amide, ester or carbonate into the backbone of a polymer. Generally, such functionalities are introduced by step growth (i.e. poly esterification) polymerisation rather than chain growth (i.e. free radical and ionic) polymerisation. The limitations of step growth polymerisation are that (a) very high conversion is required for high molecular weight polymers and (b) elimination products, such as, water or HCl are formed and require removal. In contrast, chain growth polymerisation results in very high molecular weight polymers from the beginning of the polymerisation.
There are many types of ring-opening monomers available for ionic polymerisation. However, there are only a limited number of ring-opening monomers available for free radical polymerisation. A review by Endo et al. in Chapter Five of New Methods for Polymer Synthesis, Plenum Press, New York, 1992 summarises the present state of the art. The major types of free radical polymerisation ring-opening monomers are vinyl cyclopropanes, cyclic vinyl ethers, cyclic ketene acetals (U.S. Pat. No. 4,857,620) spiro ortho esters and spiro ortho carbonates.
Many of these known ring-opening monomers suffer from limitations. Ring opening of the vinyl cyclopropanes is a reversible process and substituents that favour ring opening may also inhibit polymer growth by excessive stabilisation of the ring-opened propagating radical. The oxygenated ring-opening monomers can also exhibit sensitivity to trace amounts of acid. This results in difficulties with their synthesis and subsequent storage. Furthermore, ring opening is not guaranteed and the final polymers can contain various proportions of opened and unopened rings. In addition, the spiro ortho esters and spiro ortho carbonates have the following problems as described in Expanding Monomers, Eds. Sadhir, R. K. and Luck, R. M., CRC Press, Boca Raton, 1992:
(i) They are sensitive to impurities. Impurities can prevent ring opening from occurring and make the polymerisation somewhat irreproducible.
ii) They have a low reactivity towards free radical polymerisation. This is partly due to side reactions, such as degradative chain transfer, in the polymerisation of allylic monomers.
iii) They have a low reactivity ratio with common commercial vinyl monomers, such as, styrene, methyl methacrylate and other monomers having a similar reactivity.
iv) They are crystalline compounds with low solubilities in organic solvents and monomers.
International Patent Application No. PCT/AU93/00667 discloses new cyclic acrylate monomers which undergo facile ring opening. These compounds are readily co-polymerised with monomers that co-polymerise with acrylates or styrenic monomers.
Some compounds within the scope of the present invention have been previously reported in the following references:
(1) Butler, J.; Kellogg, R. M.; van Bolhuis, F., xe2x80x9cFunctionalized Thia-crown Ethers. Synthesis, Structure and Properties.xe2x80x9d, J Chem Soc., Chem Comm., 1990, 282;
(2) Tostikov, G. A.; Kanzafarov.F, Ya.; Kanzafarova, S. G.; Singizova, V. Kh., xe2x80x9cNucleophilic Thialation of Allyl Halides in the Presence of Phase-Transfer Catalystsxe2x80x9d., Z. Org. Khim, 1986, 22(7), 1400;
(3) Martinetz, D., Hiller, A., xe2x80x9cPhase Transfer-Catalytic Conversion of Unsaturated Organic Halogen Compounds with Sodium Sulfide Nonahydrate.xe2x80x9d, Z. Chem., 1978, 18(2), 61;
(4) Dietrich, E-M.; Schulze, K.; Muhlstadt, M., xe2x80x9c1,5-Dithiacyclanesxe2x80x9d, East German Patent No. 100 001., Sep. 5, 1973; and
(5) Richter, H.; Schulze, K; Muehlstaedt, M., xe2x80x9cReactions of 1,3-Dichloro-2-methylenepropanexe2x80x9d, Z. Chem., 1968, 8(6), 220.
References (1) to (5) are sparse in detail other than stating that the compound was made, together with a brief description of its synthesis. The use of these monocyclic monomers in free radical polymerisation is not disclosed in these references.
We have now found new unsaturated cyclic organic compounds which are capable of undergoing free radical polymerisation. These compounds include monocyclic compounds and bicyclic compounds in which two monocyclic units are tethered together.
Allylic monomers, such as allyl acetate, generally polymerise slowly, with a low degree of conversion and low molecular weight oligomers being formed. This is largely due to the occurrence of extensive degradative chain transfer during the polymerisation.
Some of the monocyclic compounds have been previously made and reported as discussed above, but their use in free radical polymerisation has not previously been disclosed. The cyclic compounds of the present invention avoid the degradative chain transfer problems of allylic monomers by converting the initially highly reactive, non-selective carbon-centered radical into a less reactive, more selective sulfur-centered radical by rapid ring-opening.
The bicyclic compounds are new and the use of such compounds is in the replacement of conventional bi-functional monomers, such as, CR 39 and dimethacrylates. Thus, crosslinked polymers may be produced with significantly less shrinkage.
According to one aspect of the present invention there is provided compounds of the formulae: 
wherein:
R1 to R4 may be the same or different and are selected from hydrogen, halogen, optionally substituted alkyl, optionally substituted aryl, nitrile, hydroxy, alkoxy, acyloxy and ester; or R1 and R2 or
R3 and R4 together form methylene;
X is selected from sulfur, sulfoxide, sulfone and disulfide;
Y is selected from sulfur, SO2, oxygen, Nxe2x80x94H, N-alkyl, N-aryl, acyl and CR5R6 wherein
R5 and R6 are the same as R1 to R4; and
Z1 and Z2 are linking functionalities.
The compounds of Formula 1a wherein R1 to R4 are hydrogen, X and Y are sulfur and Z1 is xe2x80x94(CH2)2xe2x80x94 or xe2x80x94CH2xe2x80x94C(xe2x95x90CH2)xe2x80x94CH2xe2x80x94 are known per se and therefore excluded from the compounds of the present invention.
Preferably X is S or SO2 and Y is C(R5R6), S, O or SO2.
Suitable linking functionalities for Z1 include xe2x80x94(CRR)nxe2x80x94, xe2x80x94(CRR)nxe2x80x94Oxe2x80x94(CO)xe2x80x94Oxe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94Oxe2x80x94(CO)xe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94Oxe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94C(xe2x95x90CH2)xe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94COxe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94(Cxe2x95x90O)xe2x80x94, xe2x80x94(CRR)nxe2x80x94Sxe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94SO2xe2x80x94(CRR)mxe2x80x94, xe2x80x94(CRR)nxe2x80x94Sxe2x80x94Sxe2x80x94(CRR)mxe2x80x94, xe2x80x94(Oxe2x80x94CRRCRR)nxe2x80x94 and optionally substituted phenyl (wherein R may vary within the linking functionality and is preferably selected from hydrogen, alkyl, haloalkyl, hydroxyalkyl, hydroxy, carboxy, optionally substituted phenyl, halogen and Z2; and m and n are integers including zero).
Suitable linking functionalities for Z2 in the compounds of the Formula 1b include xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Oxe2x80x94(CO)xe2x80x94Oxe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Oxe2x80x94(CO)xe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Oxe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94C(xe2x95x90CH2)xe2x80x94(CRR)qxe2x80x94Jxe2x80x94, Gxe2x80x94(CRR)pxe2x80x94COxe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94(Cxe2x95x90O)xe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Sxe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94SO2xe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(CRR)pxe2x80x94Sxe2x80x94Sxe2x80x94(CRR)qxe2x80x94Jxe2x80x94, xe2x80x94Gxe2x80x94(Oxe2x80x94CRRCRR)pxe2x80x94Jxe2x80x94 and optionally substituted phenyl (wherein R may vary within the linking functionality and is preferably selected from hydrogen, alkyl, haloalkyl, hydroxyalkyl, hydroxy, carboxy, optionally substituted phenyl and halogen; G and J are functional groups which join Z2 to Z1 and may be selected from a bond, xe2x80x94(CRR)rxe2x80x94, xe2x80x94Oxe2x80x94, NHxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94(Cxe2x95x90O)Oxe2x80x94, xe2x80x94Oxe2x80x94(Cxe2x95x90O)Oxe2x80x94, xe2x80x94(Cxe2x95x90O)NHxe2x80x94, xe2x80x94NHxe2x80x94(Cxe2x95x90O)xe2x80x94Oxe2x80x94; and p, q and r are integers including zero). Thus, Z2 can be derived from di-functional compounds capable of reacting with a functional group, such as, hydroxy, aldehyde, ketone and carboxy from the cyclic portion of the compounds of the Formula 1a. Suitable difunctional compounds from which Z2 could be derived, include diols, for example, pentane diol; dithiols; diamines; diacids, for example, succinic and phthalic acids; dichlorosilanes, for example, dichlorodimethylsilane; diisocyanates, for example, hexamethylene diisocyanate and toluene diisocyanate; and xcex1-xcfx89 hydroxy acids.
In the above definitions, the term xe2x80x9calkylxe2x80x9d, used either alone or in compound words such as xe2x80x9chaloalkylxe2x80x9d and xe2x80x9chydroxyalkylxe2x80x9d denotes straight chain, branched or cyclic alkyl, preferably C1-20 alkyl or cycloalkyl. Examples of straight chain and branched alkyl include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, isoamyl, sec-amyl, 1,2-dimethylpropyl, 1,1dimethyl-propyl, hexyl, 4-methylpentyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 1,1 -dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,2dimethylbutyl, 1,3-dimethylbutyl, 1,2,2,-trimethylpropyl, 1,1,2-trimethylpropyl, heptyl, 5-methoxyhexyl, 1-methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, 1,2-dimethylpentyl, 1,3-dimethylpentyl, 1,4-dimethyl-pentyl, 1,2,3,-trimethylbutyl, 1,1,2-trimethylbutyl, 1,1,3-triethylbutyl, octyl, 6-methylheptyl, 1-methylheptyl, 1,1,3,3-tetramethylbutyl, nonyl, 1-, 2-, 3-, 4-, 5-, 6- or 7-methyl-octyl, 1-, 2-, 3-, 4- or 5-ethylheptyl, 1-, 2- or 3-propylhexyl, decyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- and 8-methylnonyl, 1-, 2-, 3-, 4-, 5- or 6-ethyloctyl, 1-, 2-, 3- or 4-propylheptyl, undecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-methyldecyl, 1-, 2-, 3-, 4-, 5-, 6- or 7-ethylnonyl, 1-, 2-, 3-, 4- or 5-propylocytyl, 1-, 2- or 3-butylheptyl, 1-pentylhexyl, dodecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9- or 10-methylundecyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-ethyldecyl, 1-, 2-, 3-, 4-, 5- or 6-propylnonyl, 1-, 2-, 3- or 4-butyloctyl, 1-2-pentylheptyl and the like. Examples of cyclic alkyl include mono- or polycyclic alkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl and the like.
The term xe2x80x9calkoxyxe2x80x9d denotes straight chain or branched alkoxy, preferably C1-20 alkoxy. Examples of alkoxy include methoxy, ethoxy, n-propoxy, isopropoxy and the different butoxy isomers.
The term xe2x80x9chalogenxe2x80x9d denotes fluorine, chlorine, bromine or iodine, preferably chlorine or fluorine.
The term xe2x80x9carylxe2x80x9d denotes single, polynuclear, conjugated and fused residues of aromatic hydrocarbons or aromatic heterocyclic ring systems. Examples of aryl include phenyl, biphenyl, terphenyl, quaterphenyl, naphthyl, tetrahydronaphthyl, anthracenyl, dihydroanthracenyl, benzanthracenyl, dibenzanthracenyl, phenanthrenyl, fluorenyl, pyrenyl, indenyl, azulenyl, chrysenyl, pyridyl, 4-phenylpyridyl, 3-phenylpyridyl, thienyl, furyl, pyrrolyl, indolyl, pyridazinyl, pyrazolyl, pyrazinyl, thiazolyl, pyrimidinyl, quinoloinyl, isoquinolinyl, benzofurnayl, benzothienyl, purinyl, quinazolinyl, phenazinyl, acridinyl, benoxazolyl, benzothiazolyl and the like.
The term xe2x80x9cacylxe2x80x9d either alone or in compound words such as xe2x80x9cacyloxyxe2x80x9d denotes carbamoyl, aliphatic acyl group and acyl group containing an aromatic ring, which is referred to as aromatic acyl or a heterocyclic ring which is referred to as heterocyclic acyl, preferably C1-20 acyl. Examples of acyl include carbamoyl; straight chain or branched alkanoyl such as formyl, acetyl, propanoyl, butanoyl, 2-methylpropanoyl, pentanoyl, 2,2-dimethylpropanoyl, hexanoyl, heptanoyl, octanoyl, nonanoyl, decanoyl, undecanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, pentadecanoyl, hexadecanoyl, heptadecanoyl, octadecanoyl, nonadecanoyl and icosanoyl; alkoxycarbonyl such as methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, t-pentyloxycarbonyl and heptyloxycarbonyl; cycloalkylcarbonyl such as cyclopropylcarbonyl cyclobutylcarbonyl, cyclopentylcarbonyl and cyclohexylcarbonyl; alkylsulfonyl such as methylsulfonyl and ethylsulfonyl; alkoxysulfonyl such as methoxysulfonyl and ethoxysulfonyl; aroyl such as benzoyl, toluoyl and naphthoyl; aralkanoyl such as phenylalkanoyl (e.g. phenylacetyl, phenylpropanoyl, phenylbutanoyl, phenylisobutylyl, phenylpentanoyl and phenylhexanoyl) and naphthylalkanoyl (e.g. naphthylacetyl, naphthylpropanoyl and naphthylbutanoyl]; aralkenoyl such as phenylalkenoyl (e.g. phenylpropenoyl, phenylbutenoyl, phenylmethacryloyl, phenylpentenoyl and phenylhexenoyl and naphthylalkenoyl (e.g. naphthylpropenoyl, naphthylbutenoyl and naphthylpentenoyl); aralkoxycarbonyl such as phenylalkoxycarbonyl (e.g. benzyloxycarbonyl); aryloxycarbonyl such as phenoxycarbonyl and napthyloxycarbonyl; aryloxyalkanoyl such as phenoxyacetyl and phenoxypropionyl; arylcarbamoyl such as phenylcarbamoyl; arylthiocarbamoyl such as phenylthiocarbamoyl; arylglyoxyloyl such as phenylglyoxyloyl and naphthylglyoxyloyl; arylsulfonyl such as phenylsulfonyl and napthylsulfonyl; heterocycliccarbonyl; heterocyclicalkanoyl such as thienylacetyl, thienylpropanoyl, thienylbutanoyl, thienylpentanoyl, thienylhexanoyl, thiazolylacetyl, thiadiazolylacetyl and tetrazolylacetyl; heterocyclicalkenoyl such as heterocyclicpropenoyl, heterocyclicbutenoyl, heterocyclicpentenoyl and heterocyclichexenoyl; and heterocyclicglyoxyloyl such as thiazolylglyoxyloyl and thienylglyoxyloyl.
In this specification xe2x80x9coptionally substitutedxe2x80x9d means that a group may or may not be further substituted with one or more groups selected from alkyl, alkenyl, alkynyl, aryl, halo, haloalkyl, haloalkenyl, haloalkynyl, haloaryl, hydroxy, alkoxy, alkenyloxy, aryloxy, benzyloxy, haloalkoxy, haloalkenyloxy, haloaryloxy, nitro, nitroalkyl, nitroalkenyl, nitroalkynyl, nitroaryl, nitroheterocyclyl, amino, alkylamino, dialkylamino, alkenylamino, alkynylamino, arylamino, diarylamino, benzylamino, dibenzylamino, acyl, alkenylacyl, alkynylacyl, arylacyl, acylamino, diacylamino, acyloxy, alkylsulphonyloxy, arylsulphenyloxy, heterocyclyl, heterocycloxy, heterocyclamino, haloheterocyclyi, alkylsulphenyl, arylsulphenyl, carboalkoxy, carboaryloxy mercapto, alkylthio, benzylthio, acylthio and phosphorus-containing groups.
Representative examples of the compounds of the invention wherein n is as defined above are as follows: 
According to another aspect of the present invention there is provided a polymer or co-polymer which is derived from at least one monomer of the Formula 1a and/or 1b.
The present invention also provides a co-polymer derived from at least one monomer of the Formula 1a and/or 1b and at least one monomer selected from unsaturated compounds susceptible to free radical polymerisation.
Suitable unsaturated compounds include acrylic esters or amides, vinyl esters, vinyl aromatics, olefins or dienes.
The present invention further provides the use of compounds of the Formula 1a and/or 1b as monomers or co-monomers in free radical polymerisation.
The compounds of the Formula 1a and/or 1b may be used as monomers or co-monomers in free-radical, homo- or co-polymerisations. The polymerisations may be carried out in bulk or in solution. The compounds may be co-polymerised with each other or with other monomers having a suitable reactivity, such as, for example, those monomers listed in The Polymer Handbook, Ed Brandup. The polymerisation may be initiated by any suitable known method such as, redox; photochemical, for example, camphor quinone/aromatic amine or xe2x80x9cDarocur 1173xe2x80x9d by Ciba-Giegy; or thermal (i.e. AIBN) methods.
The compounds of the invention possess the ability of being able to ring open efficiently during free radical polymerisation. They undergo essentially 100% ring opening. Unlike other allylic compounds, these compounds readily polymerise to high molecular weight polymers.
In a polymerisation process, the monomers of the Formulae 1a will ring open by undergoing xcex2-bond cleavage in the manner shown in Scheme 1 below using a monomer of the Formula 1a-1 as defined above. Similarly, the di-functional, bicyclic monomers of the Formula 1b will undergo dual ring opening to give a cross-linked network. 
Generally, polymers and co-polymers resulting from a process involving the compounds of the invention will contain the compounds of the Formula 2a and/or 2b, respectively as repeating units as shown in Scheme 2 below. 
The polymerisation process of the invention allows the manufacture of polymers with a wide range of functionalities in and attached to the polymer backbone. Such polymers are generally made by step growth polymerisation which requires that the polymerisation be taken to a very high conversion in order to obtain high molecular weights. By using the compounds of the invention alone in free radical polymerisation or as co-monomers in co-polymerisations, polymers may be prepared having controlled amounts of the repeating unit of Formula 2.
By choosing appropriate substituents and co-monomers, the monomers of the Formula 1a and/or 1b can produce polymers with a degree of crystallinity ranging from high to essentially no crystallinity. For example, a homopolymer derived from a monomer of the Formula 1a-1 forms a white crystalline polymer with a melting point of 129xc2x0 C. and a very small glass transition at xe2x88x9235xc2x0 C., but a co-polymer derived from monomers of the Formula 1a-1 and/or 1a-2 (1:1) is a white rubber like solid with a much smaller observed melting point occurring at 53.3xc2x0 C. and a marked glass transition at xe2x88x9247.5xc2x0 C. Furthermore, a co-polymer of methyl methacrylate and a monomer of the Formula 1a-1 (16:1) shows essentially no crystallinity. Thus, the mechanical properties of polymers made using monomers of the Formula 1a and/or 1b can be varied as required.
The compounds of the invention enable the production of polymers having structures not otherwise obtainable. The presence of a methylene group in a polymer formed by free radical polymerisation allows a wide scope for further processing of the polymer. By way of example, the methylene group can be used as a point of further chemical manipulation. The manipulation could be in the form of standard addition chemistry to the carbon-carbon double bond or the active methylene unit could be used as a point of grafting or crosslinking. This crosslinking could occur during polymerisation or on the final co-polymer as a separate step.
Under the appropriate conditions, homopolymers of the compounds may undergo depolymerisation. For example, the homopolymer of the Formula 1a-1 depolymerises to monomers if heated to ca. 130xc2x0 C. in dimethyl sulfoxide. This facility for depolymerisation would allow, for example, the synthesis of block co-polymers if the homopolymers were heated for example in DMSO in the presence of another monomer such as methyl methacrylate.
Thus, according to a further aspect of the present invention there is provided a process for the preparation of a block co-polymer which comprises heating a homopolymer derived from a compound of the Formula 1a and/or 1b as defined above in the presence of at least one other monomer.
The compounds of the invention may also be used to minimise shrinkage during polymerisation because of their ability to ring open. For example, the compounds of the invention show significant reductions in volume shrinkage when compared with conventional monomers of an equivalent molecular weight. The monomer of the Formula 1a-2 produces a polymer that shrinks only 6.3%. A conventional monomer of the same molecular weight would shrink in the order of 11.5%. Such a suppression of volume shrinkage has applications in polymeric coatings, adhesives, dental restorative materials, matrix resins for composites, and fabrication of optical lenses (both contact and conventional).
The bicyclic compounds of the Formula 1b, provide a method of manufacturing crosslinked polymers. They show very little shrinkage on polymerisation due to their high molecular weight and the fact that they are dual ring opening. Thus, they may act as replacements in applications which use conventional di-functional monomers such as CR 39, mono-, di- or tri-ethylene glycol dimethacrylates and BIS-GMA. For example, a common resin system used in dental composites is a mixture of triethyleneglycol dimethacrylate and BIS-GMA. Such a mixture may be replaced with a resin system involving one or more compounds of the Formula 1b, for example, Ib-1, Ib-2, Ib-3 or Ib-4. Similarly, replacement of CR 39 in optical lenses manufactured by a monomer of the Formula 1b may not only result in less polymerisation shrinkage, but the resulting material may have a significantly higher refractive index due to heavy atoms, such as, sulfur in the polymer. Thus, the lenses can be more easily cast and be thinner for a given optical power. An additional advantage of resin systems composed of compounds of the Formula 1a and/or 1b is that they should readily co-polymerise with approximately equal reactivity with other compounds of the Formulae 1a and 1b for a given set of substituents R1 to R4.
In another embodiment the present invention there is provided the use of a compound of the Formula 1a and/or 1b defined above in the manufacture of adhesives, dental composites or optical lenses.
The present invention also provides an adhesive, dental composite or optical lens which is composed wholly or partly of a polymer of co-polymer as defined above.
The present invention further provides a method for the manufacture of an adhesive, dental composite or optical lens which comprises free radical polymerisation of a compound of the Formula 1a and/or 1b as defined above.
The compounds of the invention are stable chemicals and can be kept at room temperature without an inhibitor although preferably they should be refrigerated. They also are stable to mildly acidic or basic conditions and can be prepared from commercially available starting materials. It will be appreciated that a number of possible synthetic routes to the compounds of the invention can be devised in addition to those described herein or in the literature.
Thus, according to another aspect of the present invention there is provided a process for the preparation of a compound of Formula 1a and/or 1b as defined above which comprises reacting 2-chloromethyl-2-propene with a suitable xcex1-xcfx89-dimercapto compound, such as, for example, 1,2-ethanedithiol.
According to a further aspect of the present invention there is provided a process for the preparation of a compound of Formula 1a and/or 1b as defined above which comprises reacting 2-mercaptomethyl-3-mercapto-1-propene with a suitable xcex1-xcfx89-dihalo compound, such as, for example, 1,2-dibromoethane.
Compounds of Formula 1a may also be made from other compounds of Formula 1a, for example, Compound 1a-15 may be made by reacting Compound 1a-4 with methacryloyl chloride.
The present invention also provides a process for the preparation of a compound of Formula 1b as defined above which comprises reacting a compound of Formula 1a as defined above with a suitable difunctional compound, such as, a dichlorodialkylsilane, diisocyanate, dicarboxylic acid or diacid chloride, for example, oxalylchloride.